1. Field of the Invention
This invention relates to regulated DC voltage supplies. More particularly, this invention relates to solid-state (IC) regulators capable of maintaining a substantially constant DC output voltage in the face of temperature variations.
2. Description of the Prior Art
Conventional prior-art regulated voltage supplies commonly have included an internal reference source and an error amplifier arranged to compare the reference voltage with a pre-set fraction of the regulated DC output voltage. The output of the error amplifier is directed to a control element, such as a controllable impedance or the like, arranged to adjust the output DC voltage so as to maintain the two compared voltages equal. Fluctuations in the DC output voltage are thereby reduced.
In transistorized voltage-regulator circuits, the reference source typically has been a Zener diode. However, as is known in the art, Zener diodes have certain inherent characteristics which undesirably restrict the capability of a voltage regulator. An alternative type of solid-state regulator has been developed which does not use a Zener diode reference, relying instead on certain temperature-dependent characteristics of the base-to-emitter voltage (V.sub.BE) of a transistor.
U.S. Pat. No. 3,617,859 discloses a circuit of the latter type which includes a diode-connected transistor operated at one current density, and a second transistor operated at a different current density. These two transistors are interconnected with associated circuitry so as to develop a voltage proportional to the difference in the respective base-to-emitter voltages (.DELTA.V.sub.BE). This difference voltage has a positive temperature-coefficient (TC), and is connected in series with the V.sub.BE voltage of a third transistor, having a negative TC, to produce a composite resultant voltage which serves as the output of the regulator. Since the temperature coefficients of the two individual voltages are of opposite sign, the output voltage can be made relatively insensitive to temperature variations by proper choice of certain parameters.
Although such regulators based on the V.sub.BE characteristic of transistors have significant advantages, the circuit arrangements proposed and used heretofore suffer from serious limitations. It is a principal object of the present invention to provide a solid-state voltage regulator which avoids or significantly minimizes such limitations of prior art regulators.